1. Field of the Invention
The present invention relates to a light wave interference length-measuring apparatus, and more particularly to a light wave interference length-measuring apparatus which can remove measuring errors caused by a flicker of the atmosphere.
2. Description of the Prior Art
The measuring method utilizing a light wave interference has been extensively used as a highly precise measuring means, and many apparatuses are available in markets. A reference unit of the measuring according to this method is a wavelength of light. If the wave length is varied, the measuring precision is directly affected thereby, and therefore, it is important to maintain stability of the wave length in order to maintain the measuring precision.
However, where the measurement is effected in the atmosphere, the wave length is varied due to the flicker (including those caused by a change in weather as taken in terms of macroscopic changes to fine wind) of the atmosphere, resulting in the occurrence of measuring errors. This comprises a common drawback of a light wave interference measuring method. To cope with the macroscopic change in weather, it is possible to monitor the conditions of atmosphere such as atmospheric pressure, temperature, humidity and the like and correct a variation in wave length by calculation or other means. Apparatuses having such a processing function as described have been marketed.
As for the microscopic flicker, it is difficult to monitor the atmospheric conditions at various positions of a light path in real time, and therefore satisfactory correction of the wave length cannot be carried out. In the field of measurement of long distance, an attempt has been reported in which more than two different wave lengths are used, and the dispersion characteristics of the atmosphere are utilized to correct the measuring errors caused by the flicker of the atmosphere. According to the aforesaid proposal, the light intensity is modulated by a microwave, which is extremely complicated in construction and is not suitable for measurement of a short distance.